Vision based navigation systems are typically affixed to a vehicle and can perform two tasks. First, the vision based navigation system can generate a map of the vehicle's operating environment using landmarks within the operating environment. Second, the vision based navigation system can estimate the vehicle's navigation solution relative to the landmarks in the map as the vehicle operates in the environment. The vehicle's navigation solution can be defined by specifying the relative position, velocity, and three-dimensional angular orientation of two reference frames.
The number of landmarks that can be used to build the map and calculate the vehicle's navigation solution is limited to the number of landmarks that can be identified from a sensor measurement. Further, as the vehicle moves in its operating environment, the sensor affixed to the vehicle will have a different view of the local environment providing the vision based navigation system with different line of sight vectors to landmarks to calculate the navigation solution. However, as the vehicle moves, the number of useable landmarks identified in the sensor measurements and used to calculate the navigation solution can grow very large. In some real-time applications, the vehicle lacks the onboard computational capability to use an arbitrary number of landmark measurements when calculating the navigation solution using the vision based navigation system. These computational constraints effectively limit the number of landmarks that can be used to build the map and compute the vehicle's navigation solution relative to the map.